Ok, you have the mass of your leg and the condition of your muscles to consider. Assume you are average fitness wise and compare your leg force to say, a kick boxer. I know you say stomp, but please bear with me, as kick force figures are easy to obtain.
Stomping a bug
The tae kwon do spinning back kick delivered more than 1,500 pounds (680.4 kilograms) of force, while the kung fu flying double kick produced about 1,000 pounds (453.6 kilograms) of force.
But the undisputed winner practices a discipline known for its ability to deliver a knockout: Muay Thai, also known as Thai boxing.
Melchor Menor, a former two-time Muay Thai world champion, uses a simple technique to incapacitate his opponents: a knee to the chest at close quarters.
Menor himself was surprised at how powerful this move can be.
"I wasn't expecting to have the highest force. When he said the power of the knee [kick] was equal to the power of a 35-mile-an-hour [56.3-kilometer-an-hour] car crash, it was humbling."
I hope you are happy with yourself, although that's a biggish bug :)
These kick boxers train properly, work out every day and you will have to compare yourself with them, and allow for the fact that you would not use as much full out force as they do, as the bug was not an opponent or a threat, just an instinctive stomp on your part.
So its a guess, say 40 kg, (based on leg weight plus stomp force) up to 160 kg max force, depending on how annoyed you were, how heavy you are and how much you work out.
You could be more accurate if you could think of a stomping activity, but it is still going to be an estimate around the same ballpark figure as above, as there are so many unknowns. In physics, being out by a factor of 3 to 10 is still considered ok, depending on the situation, until you get out the instruments and really measure.
That's a lot easier than calculations about acceleration and all the rest of it, because I don't know your physical makeup, but you do, and then rather than do calculation, do an estimate to the extreme end and then scale it back to allow for yourself.